The invention concerns a finger lever of a valve train of an internal combustion engine, said finger lever being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever having two arms between which an inner lever is arranged for pivoting relative to the outer lever, which inner lever can be coupled to the outer lever by a coupling element, the outer lever comprising on an underside in a region of a closed end, a support for the gas exchange valve, the finger lever comprising on the underside in a region of an opposite end, a complementary surface for a support element, a cam contacting means being arranged on an upper side of the finger lever.
A switchable finger lever of the pre-cited type known from DE-OS 27 53 197 likewise includes an outer lever that encloses an inner lever that is pivotable relative to the outer lever. The coupling means is configured as a latch. A drawback of this prior art considered to be generic is that it has a relatively large overall height. Further, it is to be noted that the latch mechanism has a complicated structure and requires a comparatively complex external actuation. This can cause design space problems during mounting of the finger lever.
It is an object of the invention to provide a finger lever of the pre-cited type in which the aforesaid drawbacks are eliminated.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the outer lever has a fork-shaped open configuration, the complementary surface for the support element is arranged on the inner lever, the inner lever is pivotally fixed on the arms of the outer lever between the closed end and the opposite end, only the inner lever comprises the cam contacting means that is arranged in a region of pivotal mounting of the inner lever, and the transversely displaceable coupling element extends in a region of the opposite end.
This results in the creation of a switchable finger lever that has a relatively simple structure and requires only a comparatively small design space. As a rule, such a finger lever can therefore be incorporated without complicated modifications in existing cylinder heads for non-switchable valve trains. It is to be noted further that the finger lever of the invention is relatively simple to manufacture and, compared to non-switchable finger levers, has only a slightly higher mass moment of inertia.
The proposed finger lever can also be designated as a xe2x80x9cbucklingxe2x80x9d lever because, when the outer lever is disconnected from the inner lever by the coupling element in the region of the opposite end, both points of support of the finger lever are still maintained, the cam contacting means, preferably a rolling-bearing mounted roller, however, sinks towards the cylinder head and the outer lever simultaneously pivots about its fulcrum formed on the end of the gas exchange valve, so that the opposite end of the outer lever is likewise displaced towards the cylinder head.
Preferably, both the inner and the outer lever are made by shaping out of a lightweight material such as sheet metal. This is a further contribution towards an economy of weight, material and manufacturing costs.
To minimize the mass moment of inertia, the coupling element is preferably arranged in the region of the opposite end, for example, above the complementary surface for the support element. This complementary surface is preferably made as a cup-shaped recess on the inner lever in the region of the opposite end.
According to a further proposition of the invention, an axle serves for the pivotal mounting of the inner lever on the outer lever. This axle preferably extends approximately in the region of a central transverse plane of the finger lever and is positioned by a simple fixing method like swaging in bores of the arms of the outer lever.
As already mentioned above, the cam contacting means is a roller mounted on a rolling bearing. According to the invention, this roller is arranged on the inner lever. If need be, the roller can be replaced by a sliding contact surface. It is clear that the finger lever of the invention switches off preferably between zero lift and maximum lift. With slight modifications it can also serve as a change-over switch between valve lifts.
The fork-shaped open configuration of both the inner lever and the outer lever is a further contribution towards a light-weight construction because in each case, only one end has a mass accumulation which, in the case of the outer lever, serves as a support for the gas exchange valve, and in the inner lever, forms the complementary surface for support on a support element.
The support element is preferably a hydraulic support element but a purely mechanical support element is also covered by the invention. Particularly in the case of a hydraulic configuration of the support element which eliminates the need of separate valve lash adjusting measures, hydraulic medium can be routed in a simple manner to the coupling element in the region of the opposite end, in case a hydraulic displacement of the coupling element is desired.
Further features of the invention concern advantageous-embodiments of the lost motion spring. In one embodiment, the axle protrudes on both sides beyond the outer surfaces of the outer lever, and coiled sections of a torsion spring are arranged on the protruding axle stubs. The torsion spring acts through legs on the upper surface of the outer lever and presses through a bridge portion on the inner lever. This assures a sufficiently rapid re-setting of the outer lever relative to the inner lever in the uncoupled mode of the finger lever with a running-off cam flank. Further, the spring force of the lost motion spring is dimensioned so that an undesired influence on the length of the hydraulic support element is avoided with certainty. If necessary, suitable stops can be arranged on the valve train to prevent an excessive relative displacement of the inner and the outer lever away from each other.
In place of the torsion spring being arranged on both sides, it is also possible to arrange it only on one side. Moreover, it is also conceivable to use coil springs and the like that fulfill said lost motion function.
To prevent the switchable finger lever from slipping off from at least one gas exchange valve after mounting and during operation of the internal combustion engine, it is advantageous to arrange guide walls in the region of the one end to surround the valve stem. According to a further proposition of the invention, these guide walls are configured as extensions of the arms of the outer lever and are bent onto the underside of the respective arm. Advantageously, these guide walls are made in one piece with the side walls. However, if necessary, the guide walls can also be made as separate parts and be fixed by suitable methods such as welding and the like on the underside.